Exhaust flow in a turbocharger system may be partially directed to an exhaust driven turbine to drive a compressor that delivers air into engine cylinders, while the remaining portion of the exhaust gas may be flowed via a bypass passage around the turbine to an exhaust catalyst placed downstream of the turbine. The bypass passage may include a wastegate valve that may be adjusted into an open position, thereby allowing exhaust gases to bypass the turbine and flow to the catalyst. The wastegate valve may be adjusted into a closed position that at least partially blocks exhaust flow in the bypass passage and thus most of the exhaust gas delivered from the engine is directed to the turbine. During an engine cold start, exhaust gas may be at least partially routed through the bypass passage and wastegate in order to direct exhaust flow to a front face of the catalyst, thereby enabling catalyst light off to be reached more quickly.
One example design of a wastegate valve in an exhaust passage of a turbocharger is disclosed by Grabowska in U.S. patent application 2015/0345375. Therein, a wastegate valve assembly having flow formations is provided to direct exhaust gas in a primary flow direction while reducing exhaust losses in secondary flow directions. Specifically, the wastegate includes flow formations on a valve body, supported on a valve arm that is pivotally supported on a turbine housing. Example flow formations on the valve body include a concave shaped disc, shallow ribs and an extended semi-circular surface formed on the valve body to direct exhaust flow in the primary direction.
The inventors herein have recognized potential issues with the example approach disclosed above. For example, in the valve body configured with the concave shape disc or shallow ribs, exhaust flow may fan out in multiple directions, impinging on turbocharger walls and creating turbulent flow conditions. As a result, exhaust energy may be transmitted to the turbocharger walls leading to reduced flow efficiency and energy losses. Also, since the flow fans out in multiple directions before flowing downstream, less exhaust heat may reach the catalyst and thus delayed catalyst lightoff may occur.
The inventors herein have developed a wastegate design to at least partly address the above issues. In one example design, a wastegate may be provided comprising: a valve plate including a multiplane curved surface on an interior of the valve plate, the curved surface forming a raised edge on a first side of the valve plate and a side opening on a second side of the valve plate; a passage including a constricted section positioned upstream of the valve plate and aligned with the raised edge, the valve plate positioned at an end of the passage.
In this way, the design of the wastegate may be used to improve flow efficiency and reduce energy losses in the turbocharger while improving catalyst lightoff. For example, the multiplane curved surface on the valve plate may act in conjunction with the constricted section in the passage to guide exhaust flow and increase flow velocity downstream of the wastegate. In this way, the wastegate design may confer several advantages. By directing exhaust flow downstream instead of fanning out in multiple directions, the wastegate may reduce exhaust energy losses to turbocharger walls. Further, the constricted section in the passage may allow the exhaust flow to speed up before exiting the wastegate. In this way, the wastegate valve may reduce exhaust energy losses to improve catalyst lightoff conditions while reducing fuel emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.